If you have no interest in your Lubuntu computer beyond using it for regular tasks (e.g. email, web, photo-editing) then you can stick to using graphical user applications that you pick from the system menu. That's fine! There is really no point in making your life more difficult than it is already!
However, if you want to look a little deeper into the workings of your system, there is no better place to start than at the terminal.
Why on earth would you need to use low level commands like "cd", "ls" and "mv" if you have a very capable GUI file manager, such as PCManFM?
Well, most of the time you would try to steer clear of "the dark side" and use a GUI app. But what if your system is broke and it wont boot to the desktop? You might be able to edit files and bring the poor old dear back to life via the command line interface, if only you knew how!